Stirling cycle-type thermal device servo pump

ABSTRACT

A servo pump assisting a pulsating primary pump. A Stirling cycle engine drives an expansible chamber pump in series with the primary pump. Pulses are transmitted from the primary pump to drive the displacer piston of the engine to drive the pump in phase with the primary pump.

United States Patent Beale Feb. 29, 1972 [54] STIRLING CYCLE-TYPETHERMAL DEVICE SERVO PUMP References Cited [72] Inventor: William T.Beale, Athens, Ohio UNITED STATES PATENTS [73] Assignee: ResearchCorporation, New York, N.Y. 2,746,241 5/1956 Dros et a1. [22] Filed: Man4, 1970 3,478,695 11/1969 Goranson et al ..417/379 [21] Appl. No.:16,519 Primary ExaminerRobert M. Walker Attorney-Stowe & Stowell RelatedUS. Application Data [63] Continuation-impart of Ser. No. 812,530, Mar.5, 1571 ABSTRACT 1969, 3,552,120- A servo pump assisting a pulsatingprimary pump. A Stirling I cycle engine drives an cxpansible chamberpump in series with US. Cl-.; thg primary Pul es are transmitted fromthe primary 62/6 pump to drive the displacer piston of the engine todrive the [51] Int. Cl. ..l 04b 17/00, A6lf l/OO, F25b 9/00 pump inphase with the pn'mary Pump {58] Field of Search ..4 1 7/32 1 323, 329;60/24;

62/6; 3/1, DIG. 2

7 Claims, 2 Drawing Figures Pmammrms m2 Y 3,645,649

FIG. 2

I52 INVENTOR.

WILL/AM T BEALE ATTORNEYS STIRLING CYCLE-TYPE THERMAL DEVICE SERVO iUMPThis application is a continuation-in-part application of my copendingapplication Ser. No. 8-l2,530, filed Mar. 1969, now US. Pat. No.3,552,120.

This invention relates to an improved Stirling cycle-type thermaldevice, of the type disclosed in the above application which is suitablefor use. as a servo pump to assist primary cyclical pumps andparticularly a servo pump which is suitable for assisting the heart inpumping blood.

The principles of the Stirling cycle thermal device are well known inthe art and a relatively comprehensive review of past and recentdevelopments in Stirling thermal engines and the comparison of suchengines with the Otto, Brayton, Carnot and Ericsson cycle engines isfound in Volume 68 SAE Transactions 1960, pps. 665-684.

The thermal device as disclosed in the above application generallycomprises a displacer cylinder zone; a displacer piston mounted forreciprocation in the zone; a power cylinder; a power piston mounted inthe cylinder normally mechanically independent of the reciprocation ofthe displacer piston; a working fluid in the displacer cylinder zone;means creating a pressure differential between the opposite faces of thedisplacer piston; the last-named means including means for adding heatto or removing heat from each end of the displacer cylinder zone; meansproviding a power coupling between the displacer piston and the powerpiston consisting of fluid communication conductors between one end ofthe power cylinder and one end of the displacer cylinder zone.

It is an object of the present invention to provide means to incorporatethe above-described thermal device into a servo pump for assisting aprimary cyclical pump. This is accomplished by utilizing the powerpiston of the device as a pump drive in the fluid circuit of the primarypump and then initiating the cycle of the displacer piston of the deviceby a pulse from the pressure stroke of the primary pump.

Although the thermal device servo pump of this invention can be used forgeneral application, the invention is described hereinafter asspecifically adapted for use as a heart assist pump for pumping blood.Such a device is intended for use as a portion of the circulatory systemof a human being to assist a damaged heart by providing means to reduceresistance to the pumping action of the heart.

In this invention a blood pump is placed in series with the heart and isdriven by a Stirling cycle engine, the motion of which is triggered byheart action so that the heart and the pump operate in synchronization.

The invention will be more particularly described in reference to theaccompanying drawings wherein:

FIG. 1 is a sectional view of a heart assist servo pump and associatedcircuit in accordance with the invention; and

FIG. 2 is a fragmentary view similar to FIG. 1 showing a variation inaccordance with the invention.

Referring now to FIG. 1 of the drawings, generally designates a Stirlingcycle-type servo pump in accordance with the invention connected to theleft ventrical of a heart, schematically shown at 12.

The servo pump 10 includes a housing 14 which defines a cylinder inwhich a displacer piston 18 is mounted for reciprocation.

A power piston 20 is reciprocally mounted in the housing 14 beneath thedisplacer piston 18 and drives a pump 22. The pump is provided with aninlet 24 controlled by an inwardly opening flapper valve 26 and anoutlet 28 controlled by an outwardly opening flapper valve 30.

The pump 22 comprises a housing 32 having a pump piston 34 reciprocallymounted therein to divide the housing into an upper chamber 36,communicative with the outlet 28 and a lower chamber 38 communicativewith the inlet 24. Communication between the chambers is provided bycheck valves, shown schematically at 40, through the piston 34. Thepower piston 20 drives the pump piston 34 through a hollow drive shaft42 which traverses communicating openings in adjacent portions of thehousing 14 and pump housing 32. A bellows seal 44 is disposed betweenthe shaft 42 and the openings in the housings to provide a seal betweenhousings.

The heart, the left ventricle of which is schematically shown at 12,communicates through a valved return, with the left auricle at 46 andthrough the aorta 48 is connected to the pump inlet 24. A branch duct 50also connects the heart to a diaphragm chamber 52 disposed beneath thepump 22. The chamber 52 is provided with a diaphragm 54 which dividesthat chamber into upper and lower sections 56 and 58, respectively. Aflexible bag 60 communicates with the upper section 56 for purposes tobe described in greater detail below.

The diaphragm 54 is connected to the displacer piston 18 by means of adrive rod 62 which traverses the pump 22 coaxially through the hollowdrive shaft 42 and power piston 20. A bellows seal 64 between the lowerend of the shaft 62 and the diaphragm chamber segregates the uppersection 56 of that chamber from the lower chamber 38 of the pump 22. Abellows seal 66, around the rod 62 between the lower wall of the pump 22and the piston 34, segregates the lower chamber 38 from the interior ofthe hollow drive shaft 42.

The displacer rod 62 runs through a close sliding seal 63 serving toseparate the space 76 and its varying pressure from the bounce space 75which is relatively large and has approximately constant pressure, of,for example, 2,000 p.s.i.

The remainder of the hollow drive rod space including the space withinthe bellows seals 44, 66, 64, is held at bounce space pressure by meansof a hole 77 in the drive rod between the bounce space and the interiorof the drive rod. Thus the varying pressures of the gas in space 76 actonly on the small area of the displacer drive rod 62, and do not serveto drive the displacer appreciably. The displacer is then free to bedriven by the blood pressure acting on diaphragm 54.

The upper end of the housing is provided with heaters, regenerators andcoolers, schematically shown at 68, 70 and 72, respectively, in thebypass path around the displacer piston 18. The construction, functionand operation of this portion of the thermal device is more fully setforth in the above-referred-to application, particularly in thedescription of FIG. 6 thereof. For the purposes of this disclosure, itsuffices to say that the devices 68, 70 and 72 function, when connectedto suitable sources of energy, to cool gas being circulated downwardlytherethrough by upward movement of the displacer piston 18 and to heatgas being circulated upwardly therethrough by downward movement of thedisplacer piston thereby providing a hot zone 74 in the housing abovethe piston 18 and a cold zone 76 below the piston.

The housing is charged with a gas at high pressure, such, for example,as with helium or hydrogen gas at 2,000 p.s.i. For this reason thehousing 14 is fabricated to withstand high internal pressures.

In order to provide a substantially neutral system, e.g., one in whichthere are no large biasing force acting on the pistons, spring effectsare built into one or more of the bellows seals 44, 64 and 66 to balancethe charge gas pressures on the moving parts so that they may movereadily under the influence of fluid pressure changes.

The upper section 56 of the diaphragm chamber 52 is charged with air orinert gas at ambient pressure. The bag 60 serves to equalize thepressure within the upper section with barometric changes of pressure inthe ambient zone.

With the device charged as above, the inlet 24 is connected to the aorta48, the outlet 28 to the inlet to the arterial system and the pumpchambers 36 and 38 and connecting lines are flooded with blood. Thebranch duct 50 is connected to the heart 12 and the lower section 58 ofthe diaphragm chamber is filled with blood so that pressure pulses fromthe heart can be transmitted to the diaphragm 54. The heater 68 andcooler 72 are then energized and the servo pump 10 operates as follows:

a. The heart muscle contracts and develops a positive pressure in theleft ventricle 12. b. The positive pressure is communicated through theduct 50 to displace the diaphragm 54 upwardly.

c. Upward movement of the diaphragm 54, caused by the pressuredifference between section 58 and the ambient section 56, drives the rod62 and displacer piston 18 upwardly.

. The working gas in the hot zone 74 of the thermal device is displacedthrough the regenerator 70 and cooler 72 by upward movement of thepiston 18 and is cooled thereby.

e. The reduced pressure in working gas in the cold zone 76 caused by thecooling process causes the drive piston 20 to be driven upwardly by theresulting pressure differential between the gas in the space below thepiston 20 and the gas in the cold zone.

The piston 34 of the pump 22 is drawn upwardly, closing the check valves40 and pumping blood from the upper chamber 36 through the outlet 28 tothe arterial system.

Blood is simultaneously drawn into the lower chamber 38 through theinlet 24.

g. The heart muscle relaxes at the completion of its pump strokelowering the pressure in the left ventricle 12 and therefore in thediaphragm chamber 52.

h. With the lowering of pressure in the chamber 52, the diaphragm 54,rod 62 and displacer piston 18 move downwardly driving gas from the coldzone 76 through the regenerator 70 and heater 68 heating the gas as itenters the hot zone 14.

i. With the increase in pressure caused by the heating of the workinggas, the drive piston 20 is driven downwardly.

j. Downward movement of the piston 20 drives the pump piston 34downwardly through the shaft 42 opening the .valves 40 and transferringblood from the lower chamber 38 to the upper chamber 36. The valves 30and 26 are, of course, shut during this cycle thereby isolating the pumpfrom the system to preclude overpressured return of blood to the heartor return to the pump from the arterial system.

The above cycle is then repeated on the next beat of the heart.

The device may be altered, if so desired such that the pump dischargeson the downward stroke by reversing the connections of the upper section56 and the lower section 58 of the diaphragm chamber 52 so that theventricle pressure drives the displacer downward. The arterial and aortaconnections also must be interchanged so that the blood enters through28 and leaves through 24. The direction of operation of the valves 26,30 and 40 must also be reversed for such operation.

in FIG. 2, a variation of the diaphragm chamber 52 of FIG. 1 isillustrated. in this embodiment, components thereof corresponding tolike components of the preceding Figure are indicated by the likenumerals only of the next higher order. in this embodiment, the chamber152 is provided with inlet and outlet connections 178 and 180respectively. The connections communicate, through flapper check valves182 and 184 respectively, with a lower section 158 of the chamber 152below a diaphragm 154. The operation of the diaphragm and connecteddrive rod 162 is identical to that of the embodiment of FIG. 1.

The connections 178 and 180 are connected to the left ventricle 112 of aheart through transmitting and return lines 150 and 151 respectively.

The advantage provided by the above-described variation is that a netblood circulation takes place in the lower section 158 thereby avoidingstagnation at that point. Obviously,

other methods of transmitting the pressure pulse to the diaphragm 154,such for example as, a column of inert fluid communicative with atransducer actuated by the heart beat, could function for thepurposes ofthis invention.

What has been set forth above is intended as exemplary to enable thoseskilled in the art in the practice of the invention. Obviously, thedevice has general application as a servo in any system in which a smalltriggering force is required to cause a large efiect in phase with theforce.

What is new and therefore desired to be protected by Letters Patent ofthe United Statesjs:

l. A servo pump for assisting a pulsating primary pump comprising:

a Stirling cycle engine having displacer and power piston means; anexpansible chamber pump driven by said power piston,

means connecting said expansible chamber pump in series with saidprimary pump; and 1 means for transmitting pulses from said primary pumpto initiate drive of said displacer piston to thereby actuate saidengine to drive said expansible chamber pump in phase with said primarypump.

2. A servo pump for assisting a pulsating primary pump comprising:

a Stirling cycle engine having displacer and power piston means;

an expansible chamber pump driven by said power piston,

means connecting said expansible chamber pump in series with saidprimary pump; and

means for transmitting pulses from said primary pump to initiate driveof said displacer piston to thereby actuate said engine to drive saidexpansible chamber pump in phase with said primary pump, wherein saidmeans for transmitting pulses comprises a fluid column interconnectingsaid primary pump and said engine, and means for translating fluidpressure pulses transmitted through said column to mechanical movementto actuate said displacer piston.

3. A pump in accordance with claim 2 wherein said means for translatingincludes a diaphragm bisecting a chamber with one side thereofcommunicating with said fluid column and the other with ambientpressure.

4. A pump in accordance with claim 3 wherein said means for translatingfurther includes a drive rod interconnecting said diaphragm and saiddisplacer piston.

5. A pump in accordance with claim 3 wherein said means for transmittingpulses further comprises a return fluid column and valve means provideflow from said primary pump, through said one side of said chamber andback to said primary pump through said return column.

6. A pump in accordance with claim 1 wherein said expansible chamberpump comprises a pump housing, a pump piston reciprocable in said pumphousing, means connecting said pump piston to said drive piston andinlet and outlet means communicative with said pump housing.

7. A pump in accordance with claim 6 wherein said pump piston dividessaid pump housing into inlet and outlet chambers, said inlet and outletmeans comprising check valve controlled conduits communicating with saidinlet and outlet chambers, respectively, and check valve means disposedthrough said pump piston to provide transfer of fluid from said inlet tosaid outlet chambers.

1. A servo pump for assisting a pulsating primary pump comprising: aStirling cycle engine having displacer and power piston means; anexpansible chamber pump driven by said power piston, means connectingsaid expansible chamber pump in series with said primary pump; and meansfor transmitting pulses from said primary pump to initiate drive of saiddisplacer piston to thereby actuate said engine to drive said expansiblechamber pump in phase with said primary pump.
 2. A servo pump forassisting a pulsating primary pump comprising: a Stirling cycle enginehaving displacer and power piston means; an expansible chamber pumpdriven by said power piston, means connecting said expansible chamberpump in series with said primary pump; and means for transmitting pulsesfrom said primary pump to initiate drive of said displacer piston tothereby actuate said engine to drive said expansible chamber pump inphase with said primary pump, wherein said means for transmitting pulsescomprises a fluid column interconnecting said primary pump and saidengine, and means for translating fluid pressure pulses transmittedthrough said column to mechanical movement to actuate said displacerpiston.
 3. A pump in accordance with claim 2 wherein said means fortranslating includes a diaphragm bisecting a chamber with one sidethereof communicating with said fluid column and the other with ambientpressure.
 4. A pump in accordance with claim 3 wherein said means fortranslating further includes a drive rod interconnecting said diaphragmand said displacer piston.
 5. A pump in accordance with claim 3 whereinsaid means for transmitting pulses further comprises a return fluidcolumn and valve means provide flow from said primary pump, through saidone side of said chamber and back to said primary pump through saidreturn column.
 6. A pump in accordance with claim 1 wherein saidexpansible chamber pump comprises a pump housing, a pump pistonreciprocable in said pump housing, means connecting said pump piston tosaid drive piston and inlet and outlet means communicative with saidpump housing.
 7. A pump in accordance with claim 6 wherein said pumppiston divides said pump housing into inlet and outlet chambers, saidinlet and outlet means comprising check valve controlled conduitscommunicating with said inlet and outlet chambers, respectively, andcheck valve means disposed through said pump piston to provide transferof fluid from said inlet to said outlet chambers.